The present invention relates generally to equipment for processing semiconductor wafers. More particularly, the present invention relates to a polishing belt and associated linear polisher for chemical mechanical polishing of semiconductor wafers.
Chemical mechanical polishing (CMP) is used for planarizing semiconductor wafers during processing of the wafers. Many steps in the manufacture of semiconductor devices produce a highly irregular surface of the front side of the wafer which contains the semiconductor devices. In order to improve the manufacturability of the devices on the wafer, many processing steps require planarizing the wafer surface. For example, to improve the uniformity of deposition of a metal interconnect layer, the wafer is planarized prior to deposition to reduce the peaks and valleys on the surface over which the metal is deposited.
In conventional planarization technology, a semiconductor wafer is supported face down against a moving polishing pad. Two types of polishing or planarizing apparatus are commonly used. In rotary planarizing technology, a wafer is secured on a chuck and is brought into contact with the polishing surface. A flat polishing pad mounted on a rotating table forms the polishing surface. In linear planarizing technology, an endless belt travels over two or more rollers. The wafer is placed against the moving polishing surface of the belt. An example of such a system is the Teres(trademark) CMP System manufactured by Lam Research Corporation, Fremont, Calif.
A key component of a linear CMP system is the polishing belt. Conventionally, the belt includes a supporting band made of stiff material such as stainless steel. Polishing pads are attached to the stainless steel to form the polishing surface. For belts used on the Teres(trademark) CMP System manufactured by Lam Research Corporation, Fremont, Calif., typically, four pads are used on a belt approximately 93.7 inches long. In some cases, the pads have two layers, for example, a soft cushion layer and a polishing layer. The stainless steel band forms a strong, reliable support for the polishing pads. The pads have a finite lifetime, for example, 500 wafers. When the pads become worn, the pads are removed, the stainless steel band is cleaned and new pads are installed.
While the conventional linear belt technology has been very successful, room for improvement remains. For example, the replacement of the pads is time consuming and the stainless steel band must be cleaned during each replacement of the pads. Because the stainless steel band is so large and relatively inflexible, it can be difficult to handle and to store. The stainless steel of the band may be a source of metal contamination of the semiconductor wafer. It has been suggested to use an integrated fabric reinforced polishing belt, which would combine the mechanical support and the polishing layer into a single, replaceable article. Also, it has been suggested that a high strength reinforcing component is necessary to allow proper tensioning and support of the polishing layer. However, such a belt has some practical limitations, including complexity of manufacturing and cost of materials.
Accordingly, there is a need in the art for an improved polishing belt for CMP systems.
By way of introduction only, an improved polishing belt for a chemical mechanical planarization (CMP) system is formed from a single endless layer of polymeric material and excludes any supporting layer such as stainless steel or reinforcing fibers. The single endless layer can be any suitable polishing material having sufficient strength, durability and flexibility. The belt is made, for example, by hot casting in a cylindrical mold. A grooved polishing surface can be added to the belt. Further, for certain applications, the polishing layer may be combined with additional layers to tailor the polishing performance of the belt.
The foregoing discussion of the preferred embodiments has been provided only by way of introduction. Nothing in this section should be taken as a limitation on the following claims, which define the scope of the invention.